There have conventionally been proposed a large number of catalytic combustors which use catalysts having oxidative activities to fuels composed mainly of hydrocarbons and there is known a combustor which utilizes radioactive heat rays emitted from a surface of a catalyst directly or as radioactive heat supplied by way of a heat ray transmissive window.
In the conventional appliances described above, heat rays are radiated from a downstream surface of an exposed catalytic body to use the rays for heating, etc. in a type which supplies only a fuel through communicating slots of a catalyst body and allows catalytic oxidization to take place in the vicinity of the downstream surface of the catalytic body by diffusing and supplying oxygen in atmosphere, whereas heat rays are radiated from an upstream surface by way of a heat ray transmission window disposed in opposition to an upstream surface of a catalytic body to use the rays for heating, etc. in a type which allows a catalytic oxidative reaction to take place mainly in the vicinity of an upstream surface of the catalytic body by supplying a premixed gas of a fuel and air, and discharges an exhaust gas through communicating slots of the catalytic body.
The conventional catalytic combustors described above are useful for heating, but when they are used for illumination, they have defects as explained below.
That is, the catalytic combustors do not always provide high efficiencies when they are used for illumination in particular due to a fact that the heat rays which are obtained as radiation have a broad wavelength distribution ranging from the visible region (wavelengths not longer than 1 .mu.m) to the far infrared region (wavelengths not shorter than 3 to 5 .mu.m) which is variable dependently on surface temperatures of catalytic materials though they provide radiation efficiencies (ratios of obtained radioactive heat relative to reaction heat of fuels) higher than those of combustors which heat radiative materials with exhaust gases obtained by flame combustion due to a fact that the oxidative reaction of the fuels proceeds on surfaces of the catalyst bodies, the reaction heat is transferred directly to the catalyst bodies and radiated from the catalyst bodies with high efficiencies. Speaking concretely of a range within which the catalytic combustion is practically usable, an upper limit of a combustion rate of a catalyst body having a unit volume is restricted by a heat-resisting limit temperature of an active component (for example, a metal of a platinum group) carried on a catalyst layer and a lower limit of the combustion rate is restricted by a lower limit temperature at termination of a reaction due to a characteristic of the catalytic combustion that a temperature of the catalyst body is enhanced or lowered correspondingly to an amount of a fuel which reacts on a surface of the catalyst body. Though catalyst body is usable within a range from approximately 100.degree. C. to approximately 900.degree. C. in cases of fuel components such as hydrogen and carbon monoxide which are apt to be oxidized at low temperatures, lower limit temperatures of the catalyst body are 400.degree. C. to 500.degree. C. for propane, butane, kerosine which are ordinary domestic hydrocarbon fuels, and 650.degree. C. to 700.degree. C. for methane which is a main component of natural gases, whereas upper limit temperatures are on the order of 900.degree. C. for all the fuels mentioned above, whereby radioactive heats (rays) emitted from the catalyst body have broad wavelength distributions each of which has a peak at 1 to 3 .mu.m and includes components exceeding 10 .mu.m. Accordingly, radiated-ray components are usable for illumination only at several percents or low efficiencies and almost all heats are output as unnecessary heat outputs.
Even when the conventional catalytic combustors are used for heating, on the other hand, they provide radiation efficiencies (ratios of radiated heats relative to reaction heats of fuels) which are higher than those obtained by heating heat radiative bodies with exhaust gas obtained from flame combustion but limited to approximately 40 to 50%. Further, an upper limit of a combustion density (a combustion rate per apparent unit area of a main combustion surface of a catalyst body) is determined by a heat-resisting temperature of a substrate composing a catalyst body or a carried active component, and when a noble metal of the platinum series is carried as an active component on a ceramic honeycomb substrate, for example, a service heat-resisting temperature is on the order of 850 to 900.degree. C. and a combustion density is limited to approximately 10 to 15 kcal/h.multidot.cm.sup.2 though variable dependently on dissipation ratios of radioactive heat. Accordingly, it is actually obliged to suppress a combustion rate so as to keep a combustion density below this level or enlarge an area of a catalyst body, whereby it is difficult to produce a large amount of radioactive heat with a combustion chamber having a small volume.
After all, the conventional catalytic combustors are insufficient in their performance for use as portable heaters and illuminators which are to be used outdoors and it is therefore demanded to develop a combustor which has a smaller combustion chamber and produces a larger amount of radioactive heat.
For setting a catalyst body in a high temperature incandescent condition at its steady combustion state, it is necessary to preliminarily heat it up or raise its temperature until it exhibits its reaction activity. When a combustor is used intermittently, it is obliged to perform preheating and ignition operation, and wait until the catalyst material reaches its active temperature (on the order of 300.degree. C. to 500.degree. C. different dependently on kinds of fuels and conditions of use) before each use, thereby causing extreme inconvenience in practical use. Therefore, the combustor is practically operated so as to maintain the so-called standby combustion condition where a burning reaction is continued by feeding a fuel or a mixed gas at a low rate for keeping the catalyst body at a temperature in the vicinity of a minimum temperature at which the active temperature can be maintained and enhance the feeding rate of the fuel for obtaining required heat and rays in a moment for practical use of the combustor. In this standby combustion condition, however, the catalyst body is kept at a temperature lower than a region within which it is incandescent (emits visible rays),and the continuation of the combustion cannot be visually recognized, whereby even presence of the combustor which is used for illumination in a dark environment cannot be confirmed. In addition, a fair amount of combustion heat is necessary for keeping the catalyst body at the temperature in the standby combustion condition and a fuel consumption in the standby combustion condition constitutes a heavy burden on a combustor equipped with a cartridge type fuel container for outdoor use, thereby posing problems that it shortens usable time and that it requires an extraordinarily large fuel container.